Service adaptation in an ip multimedia subsystem network

ABSTRACT

A method of operating a Call Session Control Function node within an IP Multimedia Subsystem network. The method comprises establishing a first session corresponding to a first IP Multimedia Subsystem communication service using a first Application Server, receiving a request for a further session corresponding to a further IP Multimedia Subsystem communication service, and forwarding said request to a further Application Server. Said further Application Server is additionally notified that said first communication service is ongoing and of the nature of said first session.

TECHNICAL FIELD

The present invention relates to service adaptation in an IP MultimediaSubsystem network, and in particular, though not necessarily, to theintroduction and removal of IP Multimedia Subsystem communicationservices during an ongoing multi-media session.

BACKGROUND

IP Multimedia services provide a dynamic combination of voice, video,messaging, data, etc. within the same session. By growing the number ofbasic applications and the media which it is possible to combine, thenumber of services offered to the end users will grow, and theinter-personal communication experience will be enriched. This will leadto a new generation of personalised, rich multimedia communicationservices.

IP Multimedia Subsystem (IMS) is the technology defined by the ThirdGeneration Partnership Project (3GPP) to provide IP Multimedia servicesover mobile communication networks (3GPP TS 22.228, TS 23.228, TS24.229, TS 29.228, TS 29.229, TS 29.328 and TS 29.329 Releases 5 to 7).IMS provides key features to enrich the end-user person-to-personcommunication experience through the use of standardised IMS ServiceEnablers, which facilitate new rich person-to-person (client-to-client)communication services as well as person-to-content (client-to-server)services over IP-based networks. The IMS makes use of the SessionInitiation Protocol (SIP) to set up and control calls or sessionsbetween user terminals (or user terminals and application servers). TheSession Description Protocol (SDP), carried by SIP signalling, is usedto describe and negotiate the media components of the session. WhilstSIP was created as a user-to-user protocol, IMS allows operators andservice providers to control user access to services and to charge usersaccordingly.

FIG. 1 illustrates schematically how the IMS fits into a mobile networkarchitecture in the case of a Packet Switched (PS) and Circuit Switched(CS) access domains, whilst FIG. 2 illustrates the various interfacesdefined within the IMS and between the IMS and cellular and PSTNnetworks. [NB. IMS can also be deployed over other access technologies(e.g. fixed networks)]. Call/Session Control Functions (CSCFs) operateas SIP proxies with the IMS. The 3GPP architecture defines three typesof CSCFs: the Proxy CSCF (P-CSCF) which is the first point of contactwithin the IMS for a SIP terminal; the Serving CSCF (S-CSCF) whichprovides services to the user that the user is subscribed to; and theInterrogating CSCF (I-CSCF) whose role is to identify the correct S-CSCFand to forward to that S-CSCF a request received from a SIP terminal viaa P-CSCF.

A user registers with the IMS using the specified SIP REGISTER method.This is a mechanism for attaching to the IMS and announcing to the IMSthe address at which a SIP user identity can be reached. In 3GPP, when aSIP terminal performs a registration, the IMS authenticates the user,and allocates a S-CSCF to that user from the set of available S-CSCFs.Whilst the criteria for allocating S-CSCFs is not specified by 3GPP,these may include load sharing and service requirements. It is notedthat the allocation of an S-CSCF is key to controlling (and chargingfor) user access to IMS-based services. Operators may provide amechanism for preventing direct user-to-user SIP sessions which wouldotherwise bypass the S-CSCF.

During the registration process, it is the responsibility of the I-CSCFto select an S-CSCF if a S-CSCF is not already selected. The I-CSCFreceives the required S-CSCF capabilities from the home network's HomeSubscriber Server (HSS), and selects an appropriate S-CSCF based on thereceived capabilities. [It is noted that S-CSCF allocation is alsocarried for a user by the I-CSCF in the case where the user is called byanother party, and the user is not currently allocated an S-CSCF.] Whena registered user subsequently sends a session request to the IMS, theP-CSCF is able to forward the request to the selected S-CSCF based oninformation received from the S-CSCF during the registration process.

Within the IMS Service Network, Application Servers (ASs) are providedfor implementing IMS service functionality. Application Servers provideservices to end-users in an IMS system, and may be connected either asend-points over the 3GPP defined Mr interface, or “linked in” by anS-CSCF over the 3GPP defined ISC interface. In the latter case, InitialFilter Criteria (IFC) are used by an S-CSCF to determine whichApplications Servers should be “linked in” during a SIP Sessionestablishment. The IFCs are received by the S-CSCF from an HSS duringthe IMS registration procedure as part of a user's User Profile. SomeApplication servers are IMS communication service specific so, forexample, a given Application Server (a PoC AS) will be identified in theIFCs for a Push-to-talk over Cellular (PoC) service, whilst anotherApplication Server (a MMTel AS) will be identified for a multimediatelephony call service. IMS communication services themselves may beidentified by IMS communication service identifiers.

FIG. 2 illustrates the IMS Service Control (ISC) interface between an ASand an S-CSCF, as well as other interfaces within the IMS. Although theAS in FIG. 2 is shown as having only a single interface to an S-CSCF, itwill be appreciated that in practice the ISC interface will extendacross a communication network to which many (or all) of the CSCFservers of a given operator's network are connected, allowing an AS tocommunicate with all of these CSCFs. [Other entities illustrated in FIG.1 will be well known to those of skill in the art.]

A further interface (Ut) exists between the AS and the user terminal(TS23.002) although this is not shown in the Figure. The Ut interfaceenables the user to manage information related to his or her services,e.g. creation and assignment of Public Service Identities, management ofauthorisation policies that are used for example by “presence” services,conference policy management, etc.

In the case of a communication between two IMS users involving multipleIMS communication services, each IMS communication service is associatedwith its own SIP signalling and control path. A session involving threeIMS communication services is illustrated schematically in FIG. 3.Whilst SIP paths will of course share the same nodes within the IMS corenetwork (e.g. S-CSCFs), they may traverse different nodes within the IMSService Layer (i.e. ASs).

The implementation of network-based complex services made up of a numberof individual IMS communication services, or even the provision ofmultiple parallel but independent services to individual users, mayrequire the discovery by an IMS AS, involved in the delivery of an IMScommunication service, of the nature of other ongoing IMS communicationservices. Discovery may also be desirable even where a complex serviceis made up of two services of the same type as it is possible thatdifferent invocations of the same service may involve different ASs.However, according to the current IMS implementations, there is nomechanism to support this discovery.

SUMMARY

There is currently no mechanism in the current implementations to allowdiscovery by an AS (associated with an IMS communication service) of theidentity of other ASs currently serving a user. This precludes the ASfrom invoking service logic to implement interaction between plural IMScommunication services/application servers.

It is an object of the present invention to provide a mechanism toenable an IMS AS to identify IMS communication services with which auser is involved, other than the IMS communication service(s)facilitated by the AS itself.

According to a first aspect of the present invention there is provided amethod of operating a Call Session Control Function node within an IPMultimedia Subsystem network, the method comprising;

-   -   establishing a first session corresponding to a first IP        Multimedia Subsystem communication service using a first        Application Server;    -   receiving a request for a further session corresponding to a        further IP Multimedia Subsystem communication service and        forwarding said request to a further Application Server;    -   sending a notification to said further Application Server to        inform the further Application Server that said first        communication service is ongoing and to identify the nature of        said further session.

Based upon the information received by the further Application Server,the further Application Server can provide enhanced functionality tousers and network operators alike. For example, an Application Serverinvolved in one communication service can cause another concurrentservice to be terminated. A preferred implementation involves includingsaid notification within said request that is forwarded to the furtherApplication Server. This may be optimal from a signalling point of view.

In a preferred embodiment of the invention, said Call Session ControlFunction receives a service initiation request in respect of a secondIMS communication service for said user. The node determines whether afirst IMS communication service is already ongoing for the user in afirst Application Server and, if so, includes in said service initiationrequest the ‘communication service identifier’ for the ongoing first IMScommunication service. The node then forwards the service initiationrequest to a second Application Server associated with the requestedsecond IMS communication service. In a modification to this embodiment,said communication service identifier for the ongoing first IMScommunication service is included in a message distinct from saidservice initiation request, for example a SIP OPTIONS message.

Preferably, said Call Session Control Function node is a Serving CallSession Control Function node allocated to said user. Alternativelyhowever, the Call Session Control Function node may be a Proxy CallSession Control Function node, although this is perhaps not optimal.

In a typical implementation of the invention, said service initiationrequest is a SIP INVITE message.

In an embodiment of the present invention, the Call Session ControlFunction node may include an address of the one or more firstApplication Servers already serving said user. This may be in additionto including the associated communication service identifiers for theongoing first IMS communication service, or not. In the latter case, theaddress(es) may implicitly identify the associated IMS communicationservices. In an alternative embodiment, the address(es) is(are) notprovided by the Call Session Control Function node, but are obtained bythe second Application Server from a Home Subscriber Server using thecommunication service identifiers as key(s). Typically, the or eachaddress is an IP address.

A possible extension to the invention allows “backward” notification tothe first Application Servers of newly added second IMS communicationservices. This involves an already linked in first Application Serversubscribing to changes in a user's status at the Call Session ControlFunction node, e.g. using the SIP SUBSCRIBE method. The Call SessionControl Function node informs the first Application Server of changesusing the SIP NOTIFY method. In an alternative embodiment, the secondApplication Server may notify the one or more first Application Serversof the newly added second IMS communication service.

Other aspects of the invention are defined in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates schematically the integration of an IP MultimediaSubsystem into a 3G mobile communications system;

FIG. 2 illustrates schematically certain entities of the IP MultimediaSubsystem including an Application Server and a Serving Call/StateControl Function;

FIG. 3 illustrates schematically a single SIP session involving multipleparallel communication services;

FIG. 4 illustrates schematically the flow paths through the IMS for amultimedia telephony call with text media and for a PoC call;

FIG. 5 illustrates an exemplary procedure for establishing a sessioncorresponding to a first IMS communication service;

FIG. 6 illustrates an exemplary procedure for establishing a subsequentsession corresponding to a second IMS communication service; and

FIG. 7 illustrates an alternative exemplary procedure for establishing asubsequent session corresponding to a second IMS communication service

DETAILED DESCRIPTION

FIG. 4 illustrates an exemplary interaction between Push-to-Talk overCellular (hereinafter PoC) and Multimedia Telephony (hereinafter MMTel)communication services within the IP Multimedia Subsystem (IMS). Theillustrated user terminals or User Equipment (UE), identified as UE A 1and UE B 2, are each provided (in software) with an IMS/SIP client aswell as a number of IMS applications. In the illustrated example, theseapplications are a Multimedia telephony (MMTel) application and aPush-to-talk over Cellular (PoC) application. FIG. 4 also illustratesvarious components within the IMS, with the assumption that the two UEsare served by respective “home” IMS networks. UE A is registered withS-CSCFA 3a of its home network whilst UE B is served by S-CSCF_(B) 3b ofits home network (3GPP TS 23.228 (section 5.2.2.3). Required P-CSCF andI-CSCF nodes are not illustrated in the Figure.

Considering now IMS communication service establishment, the followingsteps are performed, although it will be appreciated that, where notexpressly stated, establishment steps are essentially as set out in thepre-existing standards.

-   I. UE A and UE B are engaged in a Multimedia telephony call. This    call is established using, for example, the generic procedure    illustrated in FIG. 5, details of which are as follows (only the    terminating side signalling is shown, with the assumption that the    originating side signalling is substantially similar):-   1. A SIP INVITE is sent from the originating network towards the    I-CSCF. The INVITE contains an indication that this call is for IMS    Communication Service 1 (ICS1)—in this example the service is MMTel.-   2. The I-CSCF queries the HSS to determine the address of the    S-CSCF. The HSS provides the S-CSCF address to the I-CSCF-   3. The I-CSCF forwards the INVITE to the S-CSCF address received    from the HSS-   4. The S-CSCF identifies that this is for IMS Communication Service    1 (ICS1) based upon the information in the INVITE, and using the    Initial Filter Criteria (IFCs). The IFC for IMS Communication    Service 1 (ICS1) is matched and through this the S-CSCF knows the    address of the ICS1-AS server (in this example a MMTel AS) to which    the INVITE should be sent.-   5. The INVITE is sent to the ICS1-AS server.-   6. After the ICS1-AS server has performed the necessary terminating    logic, the INVITE is returned to the S-CSCF.-   7. The S-CSCF forwards the INVITE to the P-CSCF for the registered    contact.-   8. The P-CSCF forwards the INVITE to the UE-   9. The rest of the session establishment signaling proceeds. The SIP    flow path is overlayed on the structure shown in FIG. 4 as a solid    line.-   II. At a certain point in time, UE A and UE B decide to initiate a    PoC conversation in addition to their ongoing telephony call. This    conversation is initiated following the same procedure as for the    Multimedia telephony call and involves the sending of a SIP INVITE    along the SIP flow path.-   III. When the S-CSCFA and S-CSCF_(B) evaluate the trigger    corresponding to the PoC service, they each add the MMTel    communication service identifier to the SIP INVITE, and forward the    SIP INVITE to the appropriate PoC AS 5 a,5 b (Steps A and B in FIG.    4). It is assumed in this case that an identifier of an IMS    communication service exists for MMTel; however, one may assume such    MMTel as the applicable IMS communication service in the absence of    any identifier of an IMS Communication service.-   IV. Upon receipt of the SIP INVITE, each PoC AS will issue an Sh    Read to the Home Subscriber Server (HSS) 6 a, 6 b within the same    home network (Steps C and D in FIG. 4), in order to retrieve the    address of the corresponding MMTel AS. The search key in this read    is (or is based on) the MMTel communication service either because    MMTel communication service identifier has been received, or because    the lack of an IMS communication service identifier, which is    understood as Multimedia Telephony. The PoC ASs return the INVITE to    the respective S-CSCFs (likely without keeping the received MMTel    communication service identifier) and the PoC related flow path    illustrated by the broken line in FIG. 4 is established.-   V. Once a PoC AS knows the address of the associated MMTel AS, both    entities can interact to provide a value added service to the users.    An example of interaction could be that MMTel AS decides to finish    the ongoing Multimedia telephony call.

It might be useful in some cases to retain the MMTel communicationservice identifier in the INVITE as this might be useful to another IMSnetwork. In the general case, an S-CSCF receiving a SIP INVITE will addall IMS communication service identifiers corresponding to alreadyestablished services into the INVITE. The ASs use this information toenhance the functionality that they provide. For example, a PoC AS mayknow that when a PoC service is terminated, it must terminate anyongoing MMTel services, but not an ongoing messaging service.

This procedure associated with steps II to IV is illustrated in FIG. 6as follows (where again the procedure is illustrated generally for anIMS communication service ICS2 handled by a second AS, ICS2-AS):

-   1. An INVITE is sent from the originating network towards the    I-CSCF. The INVITE contains an indication that this session is for    IMS Communication Service 2 (ICS2)—in this example the service is    PoC.-   2. The I-CSCF queries the HSS to determine the address of the    S-CSCF. The HSS provides the S-CSCF address to the I-CSCF-   3. The I-CSCF forwards the INVITE to the S-CSCF address that was    received from the HSS-   4. The S-CSCF identifies that this is for IMS Communication Service    2 (ICS2) based upon the information in the INVITE, and using the    Initial Filter Criteria (IFCs). The IFC for IMS Communication    Service 2 (ICS2) is matched and through this the S-CSCF knows the    address of the ICS2-AS (in this example a PoC AS) that the INVITE    should be sent to.-   5. The INVITE is sent to the ICS2-AS, and includes information about    which other IMS communication services are ongoing: ICS1—in this    example, information about MMTel. In particular, this information    may include an identifier of the ICS1-AS.-   6. Based upon receiving information about ongoing services, the    ICS2-AS decides that it needs to contact the ICS1-AS—in this    example, the PoC AS needs to contact the MMTel AS.-   7. It is assumed that the ICS1-AS for the subscriber is dynamically    allocated and the address of the AS stored in a central repository    such as the HSS. The ICS2-AS must therefore query the HSS-   8. The HSS provides the address of the ICS1-AS to ICS2-AS.-   9-10. The ICS2-AS contacts the ICS1-AS for service interaction    reasons. This may be to obtain information such as the state of the    ICS1 session, the type of session, etc to enable the ICS2-AS to    decide how to progress the requested ICS2 session establishment.-   11. Based upon the response in 10, the ICS2-AS decides whether to    progress the session or not. Subsequently the rest of the session    may be established.

FIG. 7 illustrates an alternative procedure for establishing the secondIMS communication service (ICS2). This procedure differs from thatillustrated in FIG. 6 in that the S-CSCF includes in the INVITEforwarded to the ICS2-AS the address of the ICS1-AS, in addition to theassociated IMS communication service identifier ICS1. Thus, there is noneed for the ICS2-AS to query the HSS for this address, and the ICS2-AScan proceed immediately to implement the service interaction logic.

It will be appreciated that ASs already provisioning services to a userwhen a new service is provisioned, may be informed of the new service byallowing the ASs to subscribe to changes in subscriber data at theS-CSCF. Thus, each time a new service is provisioned, the ASs willreceive a SIP NOTIFY message containing the appropriate IMScommunication service identifier. The procedures described here can beapplied to implement different levels of interaction between IMSCommunication Services. For example:

-   -   Service Precedence in IMS: One of a plurality of ongoing IMS        Communication Service sessions could be interrupted or        maintained if a session for another IMS Communication Service is        initiated. For example, a Push-to-talk over Cellular (PoC)        session could be interrupted if a Multimedia Telephony (MMTel)        session is established or vice versa.    -   Operator-controlled interaction in IMS: The network operator        could decide which combinations of IMS Communication Services        are allowed and which not, and could even apply different        charging mechanisms to different combinations of IMS        Communication Services (e.g. a chat session between two users is        always charged except if the same two users have a gaming        session ongoing when the chat session is established)    -   Advanced interaction between IMS Communication Services        controlled by service logic in IMS: New value-added services        could be implemented and offered by the network operator to the        end-users, based on a service logic which could implement        extended capabilities invoked only when different IMS        Communication Service sessions are established (e.g. certain        capabilities of a gaming service are launched, when an MMTel or        a PoC session are established)

It will be appreciated by the person of skill in the art that variousmodifications may be made to the above described embodiments withoutdeparting from the scope of the present invention.

1. A method of operating a Call Session Control Function node within anIP Multimedia Subsystem network, the method comprising; establishing afirst session corresponding to a first IP Multimedia Subsystemcommunication service using a first Application Server; receiving arequest for a further session corresponding to a further IP MultimediaSubsystem communication service and forwarding said request to a furtherApplication Server; and sending a notification to said furtherApplication Server that said first communication service is ongoing andto identify the nature of said first session.
 2. The method according toclaim 1, said Call Session Control Function node determining, uponreceipt of said request, whether a first IP Multimedia Subsystemcommunication service is already ongoing for the user in a firstApplication Server and, if so, including in said notification acommunication service identifier for the ongoing service.
 3. The methodaccording to claim 1, wherein said notification is included within saidrequest that is forwarded to the further Application Server.
 4. Themethod according to claim 1, said request being a SIP INVITE message. 5.The method according to claim 1, said notification being a SIP OPTIONSmessage.
 6. The method according to claim 1, said Call Session ControlFunction node being a Serving Call Session Control Function nodeallocated to a user.
 7. The method according to claim 1, saidnotification including an address of said first Application Server.
 8. Amethod of operating a Serving Call Session Control Function node withinan IP Multimedia Subsystem network, the method comprising: establishinga first session corresponding to a first IP Multimedia Subsystemcommunication service for a user, using a first Application Server;receiving a SIP INVITE message in respect of a further IP MultimediaSubsystem communication service; including in said SIP INVITE message acommunication service identifier identifying the nature of the ongoingfirst communication service; and forwarding the SIP INVITE message to afurther Application Server associated with the requested furthercommunication service.
 9. A method of controlling the provision ofcommunication services to users within an IP Multimedia Subsystem, themethod comprising: establishing a first session corresponding to a firstIP Multimedia Subsystem communication service, using a first ApplicationServer; receiving a request for a further session corresponding to afurther IP Multimedia Subsystem communication service; sending anotification to a further Application Server allocated to a user inorder to provide said further communication service, the notificationidentifying to, or being useable by, the further Application Server toidentify said first communication service; and receiving saidnotification at said further Application Server, using the informationcontained therein to modify the provision of the further communicationservice and/or to modify the execution of said first communicationservice.
 10. (canceled)
 11. An IP Multimedia Subsystem ApplicationServer for providing an IP Multimedia Subsystem communication service tousers, the Application Server comprising: an interface for receivingfrom a Call Session Control Function node a request to provide saidservice to a user and an identification of one or more othercommunication services currently provided to said user; and means forusing said identification to modify the provision of the requestedservice or an ongoing service for said user.
 12. An Application Serveraccording to claim 11, wherein said identification identifies one ormore Application Servers involved in provisioning said othercommunication services.
 13. An Application Server according to claim 12,wherein said identification is one or more addresses of the one or moreApplication Servers involved in provisioning said other communicationservices.